The present invention relates to a method and device for the determination of an analyte in a body fluid sample and providing a means of reliably incorporating calibration information when each test is conducted.
Many qualitative and quantitative diagnostic self-tests have developed in the clinical field utilizing bodily fluids from humans or animals as a sample. Many such devices have been developed for the analysis of blood glucose in humans. However, additional analytes may be found and the concentration determined if the appropriate low cost system was available.
One common means for the determination of an analyte in a body fluid sample is through the use of reflectance measurements using a spectrophotometer and test strip or by alternatively using a biosensor system. The biosensor system has been popular in more recent times because of the ability for a biosensor to use small sample sizes 3 to 5 xcexcls where as traditional reflectance systems usually require substantially more sample in the range of 5 to 10 xcexcls. However, the biosensor systems tend to be affected by numerous interference""s found in the body fluid samples whereas, the reflectance measurements tend to be less affected and therefor provide more accurate results
The need for a low cost system which permits low volume sample size utilization and accurate results is important to the diagnostic field and could make the monitoring of chronic disease applications more achievable.
The National Institute of health conducted a large scale study to evaluate the benefit of long term tight control of blood glucose monitoring. The study known as the DCCT proved that long term tight control of the blood glucose levels in patients with diabetes had a direct relationship to the health of the patient. One way for the medical profession to monitor the control of their patients is through the use of low cost, convenient monitors with memory.
Many diabetics currently use a test method described in U.S. Pat. No. 5,304,468 to Phillips et al. This system is comprised of an electronic meter and disposable dry reagent test strip. The meter reads the color change of the test strip after the blood sample has been applied and converts this to an approximate reading of the concentration of glucose in the blood sample. The test strips have some variation to them and the patient must select the appropriate calibration level prior to using the test strip to monitor their blood. In this way the meter can accommodate various strip performance issues. The system also uses a complex dual optics system to resolve the reflectance reading.
U.S. Pat. No. 4,637,403 to Garcia et al. Describes an integrated system which provides a method by which the patient lances the finger to get a sample of blood which is then used by the device to provide a reading of the blood glucose or other analyte concentration. This system uses a complex reflectance system to read the analyte level in the sample.
U.S. Pat. No. 5,279,294 to Anderson et al. describes a hand held shirt pocket device for the quantitative measurement of glucose in a blood sample. The device uses sophisticated optics and test strip system to achieve a reading.
U.S. Pat. No. 5,515,170 to Matzinger et al. Describes at the difficulties of keeping a reagent test strip aligned with an optics system.
European Patent Specification 0 351 891 B1 Hill et al. Describes an electrochemical sensor system and electrodes which are suitable for measuring the concentration of an analyte in a body fluid sample. The system requires the use of expensive electrodes and reader to determine the analyte concentration level.
U.S. Pat. No. 4,994,167 to Shults et al. describes a measuring device for determining the presence and amount of a substance in a biological fluid using electrochemical means.
U.S. Pat. No. 5,580,794 to Allen et al. describes a single use disposable-measuring device for determining the presence and amount of a substance in a biological sample using reflectance methods. The system uses optics and electronics which are mated on a single plane.
U.S. Pat. No. 5,522,255 to Neel et al. Describes a fluid dose, flow and coagulation device which uses a non-volatile electronic calibration device to check the calibration of the reagent strip.
U.S. Pat. No. 5,053,199 to Keiser et al. describes a biosensing meter with a pluggable memory key. This device uses a plugable memory key to control the operations of the meter.
The above patent disclosures are incorporated herein by reference in their entirety.
Although many improvements have been made, the cost and complexity needed to read the analyte concentration of a body fluid is still significant. The need to match calibration of a meter to the strips and the system of holding a test strip in alignment with the optics has been problematic and led to numerous errors in analyte concentration readings.
Currently, existing calibration mechanisms require the loading of a calibration chip, strip or manually inputting a calibration code into the meter. These devices can be reused numerous times resulting in errors by the patient who do not change or enter the appropriate calibration data.
In addition, a system which requires a smaller body fluid sample would make it more convenient for the patient and coupled with the improved accuracy found in reflectance devices compared to electro chemical would make the monitoring simpler and more accurate.
An additional issue is the use of test strips which are out of date. Old test strips which are expired can lead to errors and inaccurate results. By providing a means to eliminate the use of expired test strips the patients will not have to monitor the expiration date of the test strips and eliminates patient errors from using old test strips.
The invention overcomes the deficiencies found in current devices described in the prior art by providing a system which is specifically designed to focus the optical signal from the emitting source and back to the detecting device after being reflected off of a test strip which changes color based on a scalable chemical reaction. The instrument can use either focused lenses or light piping to direct the light from the emitter to the test strip reflectance surface and focus the reflected light back to the detection system. By doing this, the system permits the use of small amounts of test strip carrier to be used which reduce the amount of sample absorbed in the test strip carrier. The key to accomplishing this is to provide the means to focus the light on a small site and refocus the reflected light so that it is channeled to the appropriate detector. The means of focusing also permits the use of low cost optical components such as LED""s and photodetectors formed from raw die elements and are placed by automated placement equipment with respect to predetermined targets on the printed circuit board.
The system must also be able to accurately dock the test strip with the optics system including led, detector, lenses or light pipes. To achieve this a centerline alignment, or fixturing, system which minimizes rotation of the test strip carrier is required. The need to accurately describe the test strip performance with respect to the analyte concentration also helps accuracy.
An advantageous feature of this system is the use of small sample sizes to test for analyte concentrations. This provides a convenience to the patient not found in the prior art as to the amount of sample required for these devices is in excess of 5 xcexcls.
Another advantage is the minimization of strip to meter calibration errors by using a read writeable calibration system which prevents reuse after the test strip supply is used up, prevents inadvertent use of test strips which are older than the expiration date of the package.
Another advantage is the alignment of the test strip with the meter testing system to provide a means of reducing the error which is need to compensate for poor strip to optics alignment.
This invention provides a multi-use digital electronic instrument that is entirely self-contained. The device consist of a low cost optics system and the optics/lightpiping to provide adequate concentration of emitted and reflected light to perform a reflectance test. The system of this invention is useful in connection with the synchronized test kit and system disclosed in application Ser. No. 08/960,866 filed Oct. 30, 1997, the optics system disclosed in application Ser. No. 08/990,084 filed Dec. 12, 1997, and/or the test system disclosed in application Ser. No. 09/104,749 filed Jun. 25, 1998. The disclosures of the above patent applications are incorporated herein by reference in their entirety.